/**
 * Add edit options to each CF7 form
 */

add_action('wpcf7_add_meta_boxes', 'wpcf7ev_add_form_options');

function wpcf7ev_add_form_options() {

    add_meta_box('wpcf7ev_form_options', 'Email Verification', 'wpcf7ev_display_options', 'wpcf7_contact_form');

}

function wpcf7ev_display_options() {

    wp_mail('myemail@gmail.com', 'debug', 'adding checkbox');

    $wpcf7ev_options['active'] = 1;
?>

<input type="checkbox" id="wpcf7ev-active" name="wpcf7ev-[active]" value="1"<?php echo ( $wpcf7ev_options['active']==1 ) ? ' checked="checked"' : ''; ?> />
<label for="wpcf7ev-active">Use email verification</label>
<?php

}